Method to create LLVM IR - clang

Question

I am creating clang tool and I want to generate LLVM IR from clang AST. I am aware of -emit-llvm option that I can use to get *.ll file, but is there way to generate IR inside code? Some method that I can call that takes clang AST or AST context and returns llvm::Module? I cannot find any example that shows this.
Edited:
So I tried using CodeGenAction for this, but I can't get it to work. I end up with unresolved external symbol error. Am I missing something?
#include <clang/CodeGen/CodeGenAction.h>
#include <clang/Frontend/CompilerInstance.h>
#include <clang/Frontend/CompilerInvocation.h>
#include <clang/Basic/DiagnosticOptions.h>
#include <clang/Frontend/TextDiagnosticPrinter.h>
#include <llvm/ADT/IntrusiveRefCntPtr.h>
#include <llvm/IR/Module.h>
#include <llvm/IR/LLVMContext.h>
using namespace std;
clang::CodeGenAction * getAction(void)
{
// Path to the C file
string inputPath = "test.c";
// Arguments to pass to the clang frontend
vector<const char *> args;
args.push_back(inputPath.c_str());
// The compiler invocation needs a DiagnosticsEngine so it can report problems
clang::DiagnosticOptions opt = clang::DiagnosticOptions();
clang::TextDiagnosticPrinter *DiagClient = new clang::TextDiagnosticPrinter(llvm::errs(), &opt);
llvm::IntrusiveRefCntPtr<clang::DiagnosticIDs> DiagID(new clang::DiagnosticIDs());
clang::DiagnosticsEngine Diags(DiagID, &opt, DiagClient);
// Create the compiler invocation
clang::CompilerInvocation* CI(new clang::CompilerInvocation());
clang::CompilerInvocation::CreateFromArgs(*CI, &args[0], &args[0] + args.size(), Diags);
// Create the compiler instance
clang::CompilerInstance Clang;
Clang.setInvocation(CI);
// Get ready to report problems
Clang.createDiagnostics(&Diags.getDiagnosticOptions());
if (!Clang.hasDiagnostics())
return NULL;
// Create an action and make the compiler instance carry it out
clang::CodeGenAction *Act = new clang::EmitLLVMOnlyAction(&llvm::getGlobalContext());
if (!Clang.ExecuteAction(*Act))
return NULL;
return Act;
}
int main(void)
{
clang::CodeGenAction* Act = getAction();
// Grab the module built by the EmitLLVMOnlyAction
std::unique_ptr<llvm::Module> module = Act->takeModule();
// Print all functions in the module
for (llvm::Module::FunctionListType::iterator i = module->getFunctionList().begin(); i != module->getFunctionList().end(); ++i)
printf("%s\n", i->getName().str().c_str());
return 0;
}
Errors I got during linking:
LNK1120: 2 unresolved externals
LNK2001: unresolved external symbol "public: __thiscall clang::EmitLLVMOnlyAction::EmitLLVMOnlyAction(class llvm::LLVMContext *)" (??0EmitLLVMOnlyAction#clang##QAE#PAVLLVMContext#llvm###Z)
LNK2001: unresolved external symbol "public: class std::unique_ptr<class llvm::Module,struct std::default_delete<class llvm::Module> > __thiscall clang::CodeGenAction::takeModule(void)" (?takeModule#CodeGenAction#clang##QAE?AV?$unique_ptr#VModule#llvm##U?$default_delete#VModule#llvm###std###std##XZ)

Answer 1

In clang the code generation happens in the CodeGenModule class. There you can get the current module through llvm::Module & getModule () const. CodeGenModule handles code generation on module level while CodeGenFunction does this for a particular function. There you find Emit* functions for each node of the AST.